Prebiotics are substrates selectively utilized by microorganisms to confer health benefits to their hosts. Various prebiotics have been supplemented in standard milk formulas for infants who cannot be exclusively breastfed, aiming to provide benefits similar to those of breast milk. One of the most commonly used prebiotics is a mixture of 90% short-chain galacto-oligosaccharides and 10% long-chain fructo-oligosaccharides (scGOS/lcFOS [9:1]). Systematic review and meta-analysis were conducted to determine the effectiveness of scGOS:lcFOS (9:1) supplementation in standard milk formula for improving gastrointestinal health and immunity among healthy infants and toddlers, using parameters such as stool pH and intestinal colonization with beneficial bacteria. This systematic review was prepared in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses 2020 guidelines. Randomized clinical trials comparing scGOS/lcFOS (9:1)-supplemented formula versus placebo- or non-supplemented formula milk were eligible for inclusion. Related studies on gastrointestinal health and immunity among healthy infants up to five years old were searched from the earliest available date until February 29, 2024. Eighteen publications (number of participants=1,675) were selected for the systematic review, of which 11 were subsequently subjected to a meta-analysis. Results showed that the standard formula supplemented with scGOS/lcFOS (9:1) was well tolerated and conferred various gastrointestinal health and immunity to healthy infants and toddlers. These findings support the supplementation of standard milk formula with scGOS/lcFOS (9:1) for healthy infants and toddlers. © 2025 by The Korean Society of Pediatric Gastroenterology, Hepatology and Nutrition